Pitch control for aeronautical propeller



Dec. 3l, 1963 R. l.. FISCHER ETAL FITCH coNTRoL FOR AERONAUTICAL PROPELLER VVENTORS RICHARD L. FISCHER DAN/E @I cum/E By /fq/ AGE N T United States Patent O 3,115,938 PITCH CONTROL FOR AERONAUTICAL PROPELLER RichardI L.V Fischer, Suiiield, and Daniel P. Currie,

Somers, Conn., assign'ors toUnited Aircraft Corporation, East Hartford,.Conn., a corporation of4 Delaware Filed Aug. 18, 1961, Ser. No. 132,498- 4 Claims. (Cl. Utl-160,19)

This invention relates to aeronautical" propellers and more particularly to control mechanisms therefor.

It is an object of this invention to provide for an' aeronautical propeller, means for restraining the rate of movement toward low pitch during normal speed governing while allowing unlimited rate of pitch change movement for reversing, and whenvthe blades advance' to a higher pitch.

It is a fur-ther object of this invention tov provide in a hydraulic system of a propeller control mechanism, a restriction which restricts the flow of fluid in one direction and is shiftable when the tiuidilows in an opposite direction in such a manner as to bypass the restriction.

It is still' a further object of this invention to provide in a hydraulic system a shiftable restriction valve and a pressure actuated valve adapted to bypass the restriction valve for' allowing unlimited rate of pitchA change movement of the blades.

A particular characteristic of the turboprop, i.e., proellers driven by turbine-type power plants, is that the range of speed at which the propeller mustrotate is limited to prevent engine blowout. Thus, it becomes apparent that there is a necessity for maintaining the speed of the propeller Within this range for normal operations as well as in the eventa malfunction within the propeller occurs. It is generally well known that pitch locks, which are designed to prevent the pitch-of the propeller from reducing to a lower blade angle, have been provided for such a situation. However, it has been found that the time responsiveness for the pitch lockto engage inthe event of a malfunction is too slowso that the blades seek a blade angle which allows the propeller to speed beyond thecritical. speed range. To prevent this undesirable condition from arising, we have found that restricting the flow of fluid egressing. fromthe. pitch change motor will reduce the rate at whichV the blades seek a lower blade angle, thus maintainingthe speed of the propeller within desiredrange. However, this feature by itself is not satisfactory since it is of the utmostimportance to allow the pitch of the blades to increase as fast as possible. Furthermore, it is necessary to allow the. pitch to decrease as fast as possible when advancing the blades to the reverse position. It is wellknown to those skilled in the art that feathering is the condition wherein the blade angle is positioned parallel tothe air stream to incur the least air resistance and thatreversing is the blade angle below the low pitch stop wherein re-l verse thrust is effected. Our invention takes into account all of theserequirements and doesrso by providing inexpensive, lightweight and highly reliable mechanisms which are capable of rugged use.

It will be appreciated that the features enumerated above and other features ofv this invention will become readily apparent from the following description of` the drawing.

3,115,938 Patented Dec. 31, 1963 Now referring tothe single drawing, numeral 10 generally refers to the propeller which comprisesr dome 12, which houses servo motor or pitch change motor 14, which isattached to rotating cam 16; The rotating cam and its associated mechanism throughY suitable gear 1.8 and cooperating gear 241, attached tothe root ofthe blade 22, rotates the blades about its longitudinal axis. The roots. of the other blades (not shown) carried by the hub are synchronously rotated in a like manner; It is thus apparent that the angle of therbl'ades, i-.e., the pitch, is directly proportional` to the longitudinal positionY of pitch change motor 14. For further details of the pitch change motor, cam blades, hub, andthe operation thereof reference should be. made to the following United States patents:` Luiz' et. al. '2.,'943686,v Martin 'et al. 2,643,077, and Forman 2,477,868.

For a detailed. description of a variable pitch propeller modified toV incorporate this invention, showing and describing this. propeller prior to the modification, reference should be made'. to Handbook Operation andi Maintenance Instructions, Variable Pitch Aircraft Propeller', Model 53C5l-9, published by Hamilton StandardDifvision of United Aircraft Corporation on October 1, 1960;

Variable volume chambersv 24 and 26 are' provided on either side of the pitch change; motor for obtainin'gl the proper positioning of the motor for obtaining. the corresponding position, and hence, speed of the blade. The term speed throughout this descriptionk refers to the revolutions per unit time of the blade and not the speed of the aircraft.

As is illustrated in the schematic drawing, a speed con-y trol' mechanism for maintainingy the proper speed ofthe propeller is generally indicated by numeralt23 and serves to direct pressurized fluid to eitherside: of the servo.` piston in accordance with the speed signal generated by flyweights 30 andthe force imparted by spring 32, which is set by lever 34, which in turn is operatively connected to the pilot lever located in the cockpit of the aircraft. A second lever 35 may be employed to directly position the governor during the reverse operation. Thus, whenthe propeller is at its proper speed, no iiuidis. directed to the servo chamber. However, anyl variation from' the speed setting will cause iiuid to be-directedv from` the pump 36 through passages 38, 40, through the pilot valve; 42, Where it is directed` to either' side. of the, pitch change motor, depending. on the speed error. Iff for example, the propeller is overspeedingythis high pressurized fluid will be directed? through lines 44, 46, and 48! tol advance the blades to ahigher pitch. On the other' hand, ifthe pro peller is in an underspeed condition, fluid would be directed through lines 50, 52, 54 to cause they pitch change motor to'red'uce the-pitch of the' blade for increasing the propeller speed. Of course, when the pitch of the blades is movingin either direction, the chamber. not' receiving the pressurized iluid will be communicating to ak lower` pressureby virtueV of the position ofthe pilot valve. Thus for example, in movingto a higher pitch, chamberl 26 will be communicating to a lower pressure (drain) via lines 54, 52, SSand 60 and similarly, if.' the pitch change motor was moving to decrease thefpitch of the blades, chamber 24 would be communicating to drain via lines. 48, 46, 62, 64, 58 and 60.

In accordance with this invention, we. have provided a low pitch restriction valve between the speed governor 2'8 and the high pitch chamber 24. The ylow pitch restriction valve comprises 7a movable valve element 66 having a restriction passage 68 passing therethrough and spring 70 urging the element to its extereme left position. A bypass line 72 is connected to line 48 and communicates with the fluid passing through the restriction. Thus, when the 4blades are advancing toward low pitch and chamber 24 is connected to drain, as mentioned above, fluid will be egressing from chamber 24 through line 48, through bypass line '72 and then through restriction 68 and conducted through lines 46, 44, 62, 64, 58 and 60 to reservoir 61. Owing to the restriction, the flow is restrained which in turn restrains the movement of the pitch change motor and hence limits the rate at which the propeller blade can seek a lower blade angle.

To lassure that the restriction will not limit the rate at which the pitch increases, the valve element 66 responds to the pressure in chamber 78 so that when this pressure exceeds the forces exerted by spring 70 and the fluid acting on the opposite end surface 80, the valve element will shift to the right to allow the fluid to bypass the restriction and dump fluid from line 46 into line 48 to cause the servo motor to advance the blades to a higher pitch without restricting its movement.

The low pitch restrictor bypass valve 94 serves to assure that the restriction will not limit the rate of decrease pitch when the reversing system is actuated. This is accomplished in the following manner: When reverse is actuated, reversing valve cam 110l is positioned so las to cause abutment 112 to unseat the normally seated ball valve 114. This communicates high pressure fluid to chamber 92 behind the decrease pitch relief valve 90 and prevents the decrease pitch relief valve 90 from relieving the pressure in chamber 26. Therefore, the pressure in chamber 26 will rise above the normal setting of the decrease pitch relief valve 98. In accordance with this invention a low pitch restrictor bypass valve gener- -ally indicated by numeral 94 responds to this higher pressure. This Valve comprises valve element 96 which senses lthe increased pressure in chamber 26 through line 98 and chamber 10!! acting on the other side of the valve element. A spring 102 opposes this force and is set to hold the valve to the left whenever the pressure in chamber 26 is at or below the normal setting of the decrease pitch relief valve 90. An annular elongated passage 95' is provided in valve 94 which provides communication between chamber 104 and line 106 when the valve shifts to the right. In this position -the fluid egressing from chamber 24 of the pitch change motor 4bypasses the low pitch restriction valve 66 through ylines 48, 72, 108, annular passage 95 and line 106. Therefore, with the low pitch restrictor valve 94 actuated, the rate of decrease pitch is not limited by the restrictor valve 66 and a much faster rate of decrease pitch is permitted for the reverse function than `that normally permitted by restrictor valve 66.

As is well known in the propeller art, the propeller may be feathered because of some malfunction and it is often desirable to unfeather the propeller while in flight. Provisions .are provided to cause the blades to feather in response to the posi-tion of the governor 28 or feather bypass valve 80. The operation and details of this condition of operation are not necessary to the understanding of the present invention and for convenience have been omitted. However, for details reference is hereby made to the Fischer application Serial No. 76,747, filed by R. L. Fischer on December 19, 1960, and assigned to the same assignee.

Once the propeller has been feathered, unfeathering is initiated by energizing solenoid 82. When unfeathering, it may be desirable to reduce the pitch to a predetermined blade angle as quickly as possible and then to restrict the pitch change movement. To accomplish this, the solenoid may be timed for a predetermined duration and then tie-energized. yIn this manner energizing the solenoid will shift valve plunger 84 to unseat the ball valve 86. High pressurized pump fluid is conducted from line 83 to line 85, annular passage 87 to the decrease relief valve chamber 88 via line 89. The decrease relief valve 90, as was described above, functions to permit the pressure in line 54 to build up. The higher pressure valve acting in chamber on the underside of valve element 96 causes the valve to shift to the right to conduct the fluid in line `48 to 4line 46 by bypassing restriction valve and permitting unlimited rate of pitch change moment. Since unfeathering solenoid 82 is held in time relation, it will de-energize at a preselected time interval, thus seating ball `84 and simultaneously communicating chamber 88 to a drain or lower pressure. The decrease pitch relief valve will resume its normal operating conditions, allow the pressure in chamber to decrease, which in turn allows the bypass valve 94 to shift to the left. 11n this position the flow passing through line 48 in the pitch decreasing direction must flow through restriction `68 to effectuate a limited pitch change rate.

What has been shown by this invention is a means for limiting the rate of pitch change movement solely during a reduction of pitch during normal speed governing and yet providing means for allowing unlimited rate of pitch change movement during increasing pitch motion and reversing.

It is to be understood -that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departing from its spirit.

We claim:

1. For an iaeronautical propeller movable to a feather and reverse position, a servo device including a pair of Huid receiving chambers, a source of fluid under pressure, passage means connecting said source to said chambers, a speed governor disposed in said passage means for directing flow to one chamber or the other from said source in response to the speed of said propeller, one chamber receiving fluid from said governor through said passage means for moving the blade toward the feathe' position, a shiftable first valve having a restriction formed therein disposed in said passage means between said speed responsive means and said high pitch chamber, a spring urging said valve in one direction, a passage for admitting fluid from said high pitch chamber to act on the valve in the same direction as said spring, said valve having a reaction surface opposing said spring and shiftable against said spring when fluid is directed from said speed responsive means to said high pitch chamber, a second normally closed valve means for bypassing said restriction having a connection to the other chamber formed in said servo motor, means for reversing said blades, said second valve responsive to said reversing means for causing said second valve to open to bypass said low pitch restriction valve.

2. A servo system for a variable pitch bladed propeller in combination with la control system including coordinating means for reversing and feathering the pitch of said blades, means for governing the speed of the propeller including fluid conducting passage means, a servo motor varying the pitch of the blades, means for regulating the flow of fluid through said passage means to said servo motor, restriction means disposed in said passage means for restricting the flow of fluid to said servo motor solely in one direction and for permitting unrestricted flow of fluid to said servo motor in the other direction, means also disposed in said passage means responsive to said reversing means for bypassing said restriction means.

3. A servo system for a variable pitch bladed propeller having a servo motor including a high pitch chamber, means for controlling said servo motor including a governor, fluid passage means connected to said governor for admitting fluid to iand venting iluid Ifrom said high pitch chamber, a movable element forming a restriction passage disposed in said fluid passage means, said restriction passage of said element restricting the flow of Huid in said passage means when uid is being vented from said high pitch chamber for restraining the movement of said blades, said element movable in an unrestricted position to allow unrestricted passage of uid in said passage when fluid is admitted to said high pitch chambers to allow unlimited rate of pitch change movement of said blades, a reversing control including coordinating means for moving the blades to a reverse condition, a-nd valve means responsive to said reversing control for by- 10 2,661,806

passing said restriction passage.

4. A servo system `as deined in claim 3 including a feathering control having coordinating means, said second Valve means responsive to said feathering control solely during an unfeathering condition for bypassing said rst 5 valve.

References Cited in the file of this patent UNITED STATES PATENTS Chillson Apr. 4, 1944 Nims et al. Dec. 8, 1953 Luiz et al. July 5, 1960 

2. A SERVO SYSTEM FOR A VARIABLE PITCH BLADED PROPELLER IN COMBINATION WITH A CONTROL SYSTEM INCLUDING COORDINATING MEANS FOR REVERSING AND FEATHERING THE PITCH OF SAID BLADES, MEANS FOR GOVERNING THE SPEED OF THE PROPELLER INCLUDING FLUID CONDUCTING PASSAGE MEANS, A SERVO MOTOR VARYING THE PITCH OF THE BLADES, MEANS FOR REGULATING THE FLOW OF FLUID THROUGH SAID PASSAGE MEANS TO SAID SERVO MOTOR, RESTRICTION MEANS DISPOSED IN SAID PASSAGE MEANS FOR RESTRICTING THE FLOW OF FLUID TO SAID SERVO MOTOR SOLELY IN ONE DIRECTION AND FOR PERMITTING UNRESTRICTED FLOW OF FLUID TO SAID SERVO MOTOR IN THE OTHER DIRECTION, MEANS ALSO DISPOSED IN SAID PASSAGE MEANS RESPONSIVE TO SAID REVERSING MEANS FOR BYPASSING SAID RESTRICTION MEANS. 